The central hypothesis to be examined in this proposal is that SR-B1 must be associated with caveolae to promote selective cholesterol ester uptake and free cholesterol efflux from macrophages. Aim 1: To determine the extent to which SR-131 requires caveolae to facilitate cholesterol ester uptake and cholesterol efflux in macrophages. We have established cell lines that express only SR-131 or SR-BI and caveolin. Therefore, we can study the ability of SR-131 to mediated uptake and efflux of lipid in the presence or absence of caveolae. We will confirm our findings in human primary monocyte-derived macrophages. Aim 2: To determine the extent to which oxidized lipoproteins alter caveola structure and inhibit SR BI-dependent cholesterol flux in macrophages. This will be accomplished by assessing i) the effects of oxidized lipoproteins on the lipid composition of caveolae, ii) the effects of oxidized lipoproteins on the structure of caveolae, iii) the influence of caveolae modifications on the subcellular localization of SR-131, and iv) the effects of oxidized lipoproteins on SR-131 activity. Aim 3: To determine the effect of macrophage-specific over-expression of SR-B1 and caveolin on the development of atherosclerotic lesions in transgenic mice. This will be investigated by using transgenic mice over-expressing SR-131, caveolin, or both in macrophages by means of the macrosialin promoter. The mice will be crossbred to the atherosclerosis susceptible apoE -/- strain and the extent of atherosclerosis quantified by the size of the lesion and by the cholesterol/cholesterol ester content of the lesions.